1. Field of the Invention
This invention relates to a spark plug equipped with a pressure sensor to detect pressure appearing in a combustion chamber at the time of running an engine so as to transmit it to a microcomputer in a form of electrical signal.
2. Description of the Prior Art
This kind of spark plug has been introduced to detect pressure in a combustion chamber. This pressure is transformed into electrical signal by a pressure sensor which allows to contol timing of ignition and fuel injection with a microcomputer as an assistant to obtain an optimum output and fuel consumption.
The sensor is usually in the form of annular-shape, and inserted into a diameter-reduced portion provided between a diameter-increased portion and a male thread portion of a metallic shell in a spark plug.
An annular flange is of angle-shape in section, and inserted into the diameter-reduced portion.
The flange having a vertical inner rim and a horizontal outer rim, the inner rim is welded to the metallic shell while the inner rim supports the pressure sensor. A gasket ring is inserted into the diameter-reduced portion when the metallic shell is screwed through the thread portion to a cylinder block of an engine. The gasket ring has outer and inner diameter generally equivalent to those of the pressure sensor. The inner rim of the gasket ring is liable to interfere with the welded portion of the flange.
In this instance, tight engagement between the gasket ring and the horizontal rim of the flange, is somewhat lost to hinder the pressure of the cylinder block from sufficiently transmitting to the pressure sensor, thus reducing an output of the sensor to significant degree.
Therefore, it is an object of this invention to provide a spark plug with pressure sensor which is capable of preventing a gasket ring from interfering with a welded portion of a flange without enlarging an inner diametrical dimention of the gasket ring, thus improving an output of a sensor to maintain a precise and exact pressure detecting function for a long period of time with a relatively simple construction.
Accordingly there is provided a spark plug with pressure sensor comprising; a center electrode having a high voltage terminal; and insulator placed to enclose said center electrode to securely support the electrode; a tubular metallic shell having a diameter-increased portion, a diameter-reduced portion and a male thread portion in axially continuous relationship, said male thread portion being diametrically smaller than said diameter-reduced portion; an annular-shaped pressure sensor inserted into an outer surface of said diameter-reduced portion; an annular flange inserted into the outer surface of said diameter-reduced portion to sandwich said pressure sensor in thickness direction with an overhang portion of said diameter-increased portion; a gasket ring having outer and inner diameter substantially equivalent to those of said pressure sensor, the gasket ring being placed underside of said flange when said metallic shell is screwed through said thread portion to a stationary member such as a cylinder block of an engine; said annular flange extending its inner rim toward a center along the diametrical direction to position at a central side of an inner rim of said pressure sensor, and said inner rim being secured to said metallic shell by means of thermal fusion.